Endothelial cell procurement and deposition kit

ABSTRACT

The invention is an endothelial cell procurement and deposition kit for collecting fat from a patient, processing said fat to produce an endothelial cell deposition product, and depositing said product on the surface of a graft, all under sterile conditions established and maintained within the components of said kit comprised of: fat collection means for collecting subcutaneous fat from a patient; digestion means connectable to said fat collection means to maintain sterility during reception of said fat and for retaining said fat under sterile conditions during rinsing and digestion to produce a digested product; endothelial cell isolation means connectable to said digestion means for maintaining sterile conditions during reception of said digested product and for separating and isolating microvessel endothelial cells from said digested product to produce an endothelial cell product; cell deposition means connectable to said isolation means for maintaining sterile conditions during reception of said endothelial cell product and for depositing said cells on the surface of a graft to be implanted in a patient and facilitating implantation of said endothelial graft into a patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 690,689, filed Apr. 24,1991, now abandoned, which is a divisional of application Ser. No.356,431, filed May 24, 1989, now U.S. Pat. No. 5,035,708, which is acontinuation-in-part of application Ser. No. 244,496, filed Sep. 12,1988, now abandoned, in the names of Stuart K. Williams and Bruce E.Jarrell entitled "A Method of Treating a Synthetic or NaturallyOccurring Surface with Microvascular Endothelial Cells and the TreatedSurface Itself", which is a division of application Ser. No. 742,086,filed Jun. 6, 1985 and issued Apr. 11, 1989 as U.S. Pat. No. 4,820,626in the names of Stuart K. Williams and Bruce E. Jarrell entitled "Methodof Treating a Synthetic or Naturally Occurring Surface withMicrovascular Endothelial Cells, and the Treated Surface Itself", eachof which prior applications is assigned to Thomas Jefferson University,which is a co-assignee with Becton Dickinson and Company of the presentapplication, which applications are hereby incorporated by reference.

This application is related to copending applications Ser. No. 927,745,filed Nov. 6, 1986 entitled "Method of Determining Endothelial CellCoverage of a Prosthetic Surface"; Ser. No. 848,453, filed Apr. 4, 1986entitled "A Method of Treating a Synthetic or Naturally OccurringSurface with Collagen Laminate to Support Microvascular Endothelial CellGrowth and the Surface Itself"; Ser. No. 114,242, filed Oct. 28, 1987entitled "Method of Reendothelializing Vascular Linings", all of whichare continuation-in-parts of parent application Ser. No. 742,086, eachof which applications is assigned to Thomas Jefferson University, whichapplications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

While autologous vein remains the graft of choice, advanced vasculardisease and prior surgical intervention limit the availability ofautologous grafts. The use of synthetic grafts provides a means forrestoring blood flow to ischemic areas when no alternative is available.Commercially available grafts are far from ideal due to their inherentthrombogenicity. The transplantation of a functional endothelial celllining onto the surface of a vascular graft has proven to increasepatency rates and decrease thrombus formation on the flow surface inanimal models. Past and present studies have focused on the isolation oflarge vessel endothelial cells from vein segments, with the subsequentseeding of these cells on the graft lumenal surface. Tissue cultureadvances have also made the generation of large numbers of endothelialcells for high-density seeding on vascular prosthesis possible. Thesetechniques have major drawbacks in the clinical setting.Endothelialization occurs at a slow rate when low density seedingtechniques are applied. High-density seeding, using cultured endothelialcells requires the use of undefined media, not easily applicable to theclinical setting.

To overcome the problems associated with seeding large vesselendothelial cells on prosthetic grafts, methods for the isolation ofmicrovessel endothelial cells from autologous adipose tissue followed byhigh density seeding of a vascular prosthesis were developed.

Although microvessel endothelial cells have been shown to be capable ofendothelializing a blood-contacting surface, methods of procuring anddepositing these cells in an operating room setting present specialconsiderations. Methods currently used employ standard laboratoryequipment such as beakers, flasks, centrifuge tubes, shaker baths,pipettes, syringes, sterile hoods. For example, in Williams' andJarrell's U.S. Pat. No. 4,820,626 and related applications, methods oftreating a graft surface with endothelial cells are disclosed. Accordingto those methods, subcutaneous adipose tissue is aspirated via a cannulaand transferred by vacuum into a mucous trap. The trap is thentransferred to a sterile hood for further processing. Adipose tissue istransferred to a sieve inside a funnel which is placed in a sterilebeaker. A rinsing solution is then poured over the tissue to remove redblood cells and lysed fat. The tissue is manually poured into a sterileErlenmeyer flask containing collagenase solution and agitated at 37° C.for 20 minutes. The collagenase slurry is manually poured into sterileconical centrifuge tubes and spun for seven minutes at 700×G. Theendothelial cells ar then pipetted out of the tube. A graft is tied to amale luer extension and secured within a tube. The cells are resuspendedin serum protein media and drawn into a syringe. Using a needle and asyringe, the cells are forced into the lumen of the graft. The graft ismanually rotated for 2 hours.

In spite of these advances, a need still exists for a simple, reliablemethod of producing endothelial cell coatings on a graft in a operatingroom setting.

SUMMARY OF THE INVENTION

The present invention provides a simple, reliable kit for producing anendothelialized graft using microvascular endothelial cells harvestedfrom the patient who is to receive that graft. The subject kit isdesigned to isolate endothelial cells from human fat, to process thatfat to produce a cell deposition product, and to deposit that product onthe surface of a graft, all under sterile conditions established andmaintained within the components of the kit. The kit is a closed systemwhich lessens the likelihood of contamination and reduces the amount oflabor required and user error.

Accordingly, a primary object of the present invention is the provisionof a kit for producing endothelialized grafts for implantation inhumans.

Another object of the present invention is the provision of a systemwhich establishes and maintains sterility of harvested autologousendothelial cells during processing procedures required to produce theimplantable endothelialized vascular graft.

These and other objects of the present invention will become apparentfrom the following, more detailed description and is illustrated in itsspecific embodiment in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the fat collection unit which is used tocollect fat containing microvascular endothelial cells from the patientto receive the graft, which fat is ultimately collected into a fatcollection device;

FIG. 2 is a schematic of the digestion unit, wherein the digestiondevice is shown in association with the fat collection device of the fatcollection unit of FIG. 1, which unit is used to produce a digestionproduct which is transferred to the endothelial cell isolation device,also shown in FIG. 2;

FIG. 3 is a diagram of the endothelial cell isolation unit;

FIG. 4 is a diagram of the vascular graft processing unit and theendothelial cell deposition unit illustrating the components whichproduce the endothelial cell product and which transfer that product fordeposition on a vascular graft;

FIG. 5 is a cross-section, on a greatly enlarged scale, of the fatcollection device of FIG. 1;

FIG. 6(a) is a longitudinal cross-section, in a greatly enlarged scale,of the digestion device of FIG. 2;

FIG. 6(b) is a bottom view, in a greatly enlarged scale, of thedigestion device of FIG. 2;

FIG. 6(c) is a top end view, in a greatly enlarged scale of thedigestion device of FIG. 2;

FIG. 7(a) is an enlarged front view of the endothelial cell isolationdevice of FIG. 2;

FIG. 7(b) is an enlarged side view of the endothelial cell isolationdevice of FIG. 2;

FIG. 8 is a diagrammatic cross section of the process tube assembly,shown in FIG. 4 within the endothelial cell deposition unit, whichprocess tube assembly is used to introduce the endothelial cell productonto the interior surface of the graft lumen;

FIG. 9 is an enlarged diagrammatic cross-section of the inner and outerprocess tubes of the vascular graft processing unit illustrated in FIG.8;

FIG. 10 is a greatly enlarged side view of the components of the innerprocess tube of FIG. 9;

FIG. 11 is a greatly enlarged side view of the components of the outerprocess tube of FIG. 9;

FIG. 12 is a bar graph showing the average endothelial cell densityachieved per section of processed graft for the grafts processed usingthe preferred kit of the present invention and those using prior artmethods;

FIG. 13 is a scanning electron micrograph of a graft processed with thepreferred kit of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the preferred methods of the present invention,subcutaneous fat is removed from the patient using modified liposuctiontechniques and transferred to a self-contained, closed device where thefat can be stored under sterile conditions until needed. The fat issterilely transferred to a digestion device where it is automaticallywashed initially to remove red blood cells and other debris, followed bya controlled collagenase digestion for 20 minutes at 37° C. The fatslurry is then transferred to an endothelial cell isolation device,again under sterile conditions, where endothelial cells sediment into anisolation device, allowing automatic retrieval of the isolatedendothelial cells. The cell suspension is then sterilely transferred toa processing unit wherein the cells are rapidly filtered onto the graftsurface under sterile conditions. The endothelial cell isolation anddeposition process requires only about 40 minutes for completion usingthe kit described herein. Following an incubation period, the graft isready for implantation into the patient. In paired comparisons betweenthe kit and the methods practiced previously, equivalence andreproducibility in the number of isolated endothelial cells andadherence of the cells to graft surface have been observed. The systemyields endothelial cell product in numbers acceptable for subsequenthigh density seeding (range 5.14×10⁶ to 4.24×10⁷ cells from 50 ccs offat) and adherence to the graft surface. The kit deposits cells alongthe entire length and diameter of the graft consistently, with nosignificant difference in cell concentration a compared by analysis ofvariance. Significant advantages of the kit include 1) closed, sterilefluid path; 2) minimal user input; 3) compatibility with an operatingroom environment; 4) optimization of the conditions to a highlyreproducible process from patient to patient.

The system consists of five primary subsystems: 1) fat collection unit(see FIG. 1); 2) digestion unit (see FIG. 2); 3) endothelial cellisolation unit (see FIG. 3); 4) vascular graft processing unit (see FIG.4); and 5) endothelial cell deposition unit (see FIG. 4).

The fat collection unit (FIG. 1) collects subcutaneous fat tissue samplefrom a patient. The components include: in-flow tubing (12), fatcollection device (14), vacuum tubing (15), aspiration cannula (10) andan aspiration pump (18). The aspiration pump (18) is used to suctionsubcutaneous fat tissue from the patient through the cannula (10) andin-flow tubing (12) and into the fat collection device (14).

A preferred embodiment of the fat collection device is shown in FIG. 5.It consists of a cylindrical chamber (54) with two vacuum line ports atthe top (59 and 61) and an outlet port (60) at the bottom connected to atwo-way stopcock (62). A plunger rod (57) passes through the top of thechamber and is connected to a syringe-like stopper (56). The stopper hastwo holes through which vacuum line ports (59 and 61) pass. When theplunger is in the "down" position, a flexible rubber diaphragm (58)covers the bottom of the stopper and the holes. When the plunger is inthe "up" position, the rubber diaphragm (58) is pushed away from thebottom of the stopper by the vacuum line ports (59 and 61), thus openingcommunication between the inside of the chamber and the vacuum lines (12and 15). In order to use the device, it must be placed in line with thevacuum line of a liposuction system by using the elbow connectors (63and 65). In addition, the plunger rod must be in the "up" position.During liposuction, the device acts as a catch trap for the fat tissue.After the appropriate amount of fat is collected, the vacuum line elbowconnectors (63 and 65) are disconnected and the plunger rod (57) ispushed down. The rubber diaphragm (58) assumes its original positioncovering and sealing the bottom of the stopper as it forces the fattissue out of the outlet port. The subject device serves two functions:to collect fat and facilitate transfer to the digestion unit in asterile manner.

The digestion unit (FIG. 2) rinses the fat tissue sample with rinsesolution and digests it with the enzyme collagenase. The componentsinclude: digestion device (16), waste vessel (32) endothelial cellisolation device (30), digestion stand (17), collagenase solution IVbags/sets (20 and 22), rinse solution IV bags/sets (21 and 24), controlbox (27) for temperature and fluid transfer controls and system vacuumsource, assorted tubing connectors, air filters, valves. The fat tissueis manually transferred from the fat collection device (14) through aclosed line into the digestion device (16). The fat tissue is rinsedtherein with rinse solution introduced into the chamber from the rinsesolution IV bags/sets (21 and 24). The rinse solution is drained fromthe chamber into the waste vessel (32) after rinsing is completed. Thecollagenase solution is then transferred from the collagenase solutionIV bags/sets (20 and 22) into the digestion device (16). Digestion ofthe fat tissue by the collagenase solution occurs while the mixture isagitated with filtered air and heated to 37° C. The digested fat tissueand collagenase solution mixture is then vacuum transferred into theendothelial cell isolation device (30) for further processing.

The digestion device is shown in FIG. 6. It consists of a chamber (64)with several inlet ports at the top (66, 67, 68, 69 and 70), one ofwhich contains a filter and is connected to a tube (72) which terminatesnear the bottom of the chamber. A series of "fingers" (74) is bonded tothe end of the tube in a radial fashion. At the bottom of the chamber isa conical mesh filter (76) below which are two outlet ports (80 and 82)and a temperature probe sheath (78). During use, the collected fattissue is introduced into the chamber (64) through one of the top inletports (66) followed by rinse solution (Media 199E, Hanks, saline, PBS orother physiological buffered solution) through another of the inletports (67). A vacuum line, connected to another inlet port (68) causesfiltered air to enter through the center port (69) and tube (72) whichair bubbles up through the fat mixture creating agitation. The "fingers"(74) serve to distribute the bubbling air to ensure uniform agitationand provide a frictional surface to facilitate break-up of the fat. Therinse solution is then drawn out through the bottom of the mesh andexpelled through one of the outlet ports (80) leaving behind fat tissuerelatively free of blood. Digestive enzyme solution (collagenase,dispase, trypsin, or other tissue dissociation enzyme) is introducedthrough another of the top inlet ports (70) followed by agitation bybubbling. Throughout this process, a temperature probe (79) inside theprobe sheath (78) monitors the process temperature and sends feedback toan external heat controller within the control box (27). When digestionis complete, the digested fat solution, rich in microvessel endothelialcells, is drawn out through the bottom mesh and expelled through anoutlet port (82) for subsequent processing. The mesh (76) retainsundigested tissue and large fibrous matter which is discarded with thedevice. The subject device is a closed system which lessens thelikelihood of contamination and reduces the amount of labor and usererror.

The endothelial cell isolation unit (shown in FIG. 3) separates andisolates the endothelial cells from within the digested fat tissuesample. The components include: centrifuge (33), centrifuge shields(31), endothelial cell isolation device (30). The endothelial cellisolation device (30) is placed into a centrifuge shield and theassembly is placed into the centrifuge (33). Centrifugation isolates theendothelial cells. The endothelial cell isolation device (30) is thenplaced in line with the vascular graft processing unit and mounted onthe endothelial cell deposition unit.

The endothelial cell isolation device is shown in FIG. 7. It consists ofa primary chamber (88) tapering to a secondary chamber or ampule (90)having inlet and outlet ports (92 and 94). In line with each port (92and 94) is a two-position valve (91 and 93). The first position allowscommunication between the primary and secondary chambers. The secondposition allows communication between the secondary chamber and theoutside port. Each valve (91 and 93) is initially turned to the firstposition. Digested fat tissue is introduced through the top port (84).The device is then placed into a centrifuge and spun. Centrifugationseparates endothelial cells into the ampule (90), the dimensions ofwhich are optimized for isolating a "pellet" of endothelial cellsbetween the two ports. The valves are then turned to the second positionisolating the "pellet" from the primary chamber (88) above and packedred blood cells below. The endothelial cell "pellet" may then be flushedout by attaching a pressurized line to the inlet port (92) or vacuumline to the outlet port (94). The subject device is a closed systemwhich maintains sterility and reduces the amount of labor and usererror.

The vascular graft processing unit shown in FIG. 4 protects, maintainssterility and facilitates the processing of the graft during handling,pre-wetting and cell deposition. The components include: process tubeassembly including an inner and an outer tube (46), graft, vacuumline/trap assembly (44), vortex/mesh assembly (34), autologousserum/media solution IV bags/sets (36 and 38). The graft is mountedwithin the inner tube of the process tube assembly. The purpose of theouter tube is to maintain sterility of the inner tube. The graft ispre-wetted prior to cell deposition by drawing the autologousserum/media solution from an IV bag, through the vortex/mesh assembly,into the lumen of the graft, and out through the graft wall until allair is purged from the inner tube of the process tube assembly. Thegraft processing unit is then transferred to the endothelial celldeposition unit.

The fully assembled process tube is shown in FIG. 8. It consists of twomajor assemblies: inner process tube (100) and outer process tube (112)(see FIG. 9). As shown in FIG. 10, the inner process tube consists ofthe following sub-assemblies: vent cap (104), handle cap (108), innerprocess tube body (102), tunneler (110), tunneler tip (106). A graft isthreaded through the lumen of the tunneler (110) and is attached to thehandle cap (108) prior to assembly. As shown in FIG. 11, the outerprocess tube consists of the following subassemblies: outer process tubebody (113), inflow endcap (116), outflow endcap (114). In its fullyassembled form, the process tube assembly serves the followingfunctions: it houses, protects and maintains sterility of the graftduring shipment and handling in the operating room; it supports thegraft and allows fluid access to the graft lumen duringendothelialization; it breaks down into a sub-assembly which facilitatesimplantation of the graft while protecting the endothelial lining.During endothelialization, the inflow endcap of the device (116) isconnected to a container of endothelial cell suspension, and the outflowendcap (114) is connected to a vacuum source in the control box (27).Negative pressure external to the porous graft causes the endothelialcell suspension to flow into the graft lumen and out through the wallthereby filtering endothelial cells onto the inner graft wall. Thefiltered solution continues to flow out through the holes (111) in thetunneler wall (110) and out of the vent cap (104). During thisoperation, the device may be rotated about its central axis by theaddition of rotary fittings at the outer process tube end caps. Afterendothelialization is complete, the inner process tube (100) is removedfrom the outer process tube (112) and the handle cap (108)/tunneler(110)/tip (106) assembly is removed from the inner process tube body(102). The graft may then be "tunneled" through, for example, thepatient's leg tissue for proper graft placement without contacting ordisturbing the graft. Once positioned, the handle cap (108) is detachedfrom the tunneler (110) and the tunneler (110) is withdrawn, leaving thegraft in place for the distal anastomosis. An IV line containingautologous serum media solution may be connected to the handle cap (108)to maintain wetting of the graft lumen during surgical placement. Whenthe distal anastomosis is completed, the graft is snipped at theproximal end, releasing it from the handle cap (108) and readying it forthe proximal anastomosis.

The endothelial cell deposition unit shown in FIG. 4 promotesendothelial cell deposition onto the lumen of the graft. The componentsinclude: process tube rotation fixture (48), insulated trough (50),heating pad (52), water circulator/heater (53). The process tubeassembly (46) is positioned on the rotation fixture within the insulatedtrough and wrapped in the heating pad which is heated by the watercirculator. The cell deposition procedure is initiated by using vacuumto draw autologous serum/media solution and the isolated endothelialcells from endothelial cell isolation device (30). The endothelial cellsand autologous serum/media solution pass through the vortex/meshassembly (34) which breaks up the endothelial cell pellet and filtersout gross particulate. The endothelial cells resuspended in the solutionare pressurized into the lumen of the graft. The graft filters thesolution leaving endothelial cells on the luminal wall. Duringpressurization, and subsequent cell-graft association, the graft isrotated about its central axis at a constant rate and maintained at 37°C.

Ancillary items include: blood collection bag and transfer bag withoutanticoagulant to be used for blood collection and serum separation, theserum to be used for the make-up of autologous serum/media solution andan additional solution IV bag filled with autologous serum/mediasolution and an administration set to be used to maintain the cellsduring graft implantation.

EXAMPLE 1

Microvascular endothelial cells were isolated and deposited on 4 mm×80cm expanded polytetrafluoroethylene (ePTFE) grafts using both the kitand patented methods. After a two hour rotation, the grafts were rinsedwith media and cut into 8 sections. P1 is where the cells wereintroduced and P8 is the opposite end. The graft segments werehematoxylin stained and the cells counted using an automated imageanalysis system. FIG. 12 provides the average cell density achieved persection on such Gore-Tex® tubular grafts.

EXAMPLE 2

Endothelial cell product was prepared and deposited on an ePTFE graftusing the kit. A scanning electron micrograph of the microvascularendothelial cells deposited on the graft is shown in FIG. 13. Theendothelial cell product was consistently deposited along the entirelength of the graft with no significant variation in cell concentration.

As seen from the above a simple, reliable kit for producing anendothelialized graft using microvascular endothelial cells is provided.These cells are harvested from a patient who is to receive the graft andprocessed through the use of kit which isolates those cells to producecell deposition product, and deposits that product on the surface of agraft, all under sterile conditions established and maintained withinthe components of the kit.

While the foregoing description has been directed to the preferredembodiment kit of the present invention, those of ordinary skill in theart in this field will appreciate that various modifications can be madein the materials and methods described herein without departing from thescope of the present invention, which is defined more particularly inthe claims appended hereto.

What is claimed:
 1. A fat collection device, comprising:a chamber havinga top and a bottom; a stopper means for sealing the chamber, capable ofbeing slidably raised and lowered with respect to said chamber; an inlettube extending in sliding engagement through said stopper into saidchamber; a vacuum inlet tube extending in sliding engagement throughsaid stopper means into said chamber; a plunger means connected to saidstopper means for lowering and raising said stopper means relative tothe chamber, the inlet tube and the vacuum inlet tube; a diaphragm meansaffixed to said stopper means for sealing said chamber during fattransfer, said diaphragm means being deflected by said inlet tube andsaid vacuum inlet tube when said stopper means is in a raised positionand closing off both said inlet tube and said vacuum inlet tube when thestopper means is in a lowered position, thereby facilitating fattransfer from the chamber; and an outlet disposed at the bottom of thechamber, said outlet including a valve for regulating the transfer offat from the chamber.
 2. Apparatus for collecting fat cells from asubject comprising:a chamber for retaining fat cells; a cell inlet portopening into the chamber for providing selective communication betweenthe chamber and a source of fat cells; a vacuum inlet port opening intothe chamber for providing selective communication between the chamberand a vacuum source; a first valve comprising apparatus moveable betweentwo positions, a first position controlling the selective communicationbetween the cell inlet port and the chamber, and the second positioncontrolling the selective communication between the vacuum inlet portand the chamber; and a cell outlet port opening into the chamber forproviding selective communication between the chamber and a steriledevice, whereby the flow of cells through the apparatus is maintainedunder conditions of sterility.
 3. The apparatus of claim 2, wherein thefirst valve comprises a diaphragm for selectively sealing the cell inletand vacuum inlet ports.
 4. The apparatus of claim 3, further comprisinga stopper slidably disposed within the chamber and movable with acontrol rod, and wherein the cell inlet and vacuum inlet ports eachcomprises a tube extending into the chamber through the stopper, andwherein the diaphgram is attached to the plunger, whereby upon movingthe plunger with the control rod, the diaphragm selectively seals thecell inlet and vacuum inlet ports.
 5. The apparatus of claim 2, whereinthe cell outlet port comprises a second valve.